Clicking “reply” now means that only joint followers see the tweet even if you prefix it with a “.” (or anything else for that matter). You can still tweet at (@) someone with a “.@” construction and have all your followers see it but not if you click reply. When did this change occur? I cannot find anything on the internet that documents it. Is this the first post to do so?
I have seen a lot less of these types of replies and I thought he may be wrong — until I saw that a few were using a work around: not hitting the reply button instead creating a new tweet. What a pain in the ass.